Generally, a magnetic recording medium comprising a non-magnetic support having thereon a magnetic layer comprising ferromagnetic particles dispersed in a binder is used as a magnetic recording medium, for example as an audio tape, a video tape, or a computer tape.
In response to recent demand for high density recording, the size of ferromagnetic particles has been decreased, the dispersibility of ferromagnetic particles increased, the surface property of a magnetic layer increased, and the packing density of ferromagnetic particles increased.
In order to increase the dispersibility of ferromagnetic particles, dispersing agents are used with magnetic coating compositions.
JP-A-61-123017 (the term "JP-A" as used herein means an unexamined published Japanese patent application) shows that a polyurethane resin containing metal sulfonates and a vinyl chloride resin are used as a binder, namely, polar groups can be introduced into a binder, thereby increasing dispersibility.
JP-A-63-98834 discloses that in order to improve the surface property of a magnetic layer a calender treatment is carried out at a higher temperature or pressure, and also the surface of a magnetic layer is ground with a grinding tool.
JP-A-63-259830 proposes that in order to provide a magnetic recording medium in which head clogging and dropouts hardly take place, the surface of a magnetic layer is polished with a polishing tape. Consequently, it turns out that the number of ferromagnetic particles decreases at the surface of the magnetic layer, with a result that dropouts and head clogging decrease. However, when the crystallite size of ferromagnetic particles becomes 250 angstroms or less, sufficient effects cannot be obtained by the above polishing methods.
Magnetic recording media for higher density recording in which electromagnetic characteristics are taken seriously are generally liable to be characterized by decreased running property and durability. Particularly, a magnetic recording medium for higher density recording is liable to significantly increase video head clogging (which means that dirt adheres to a video head, thereby lowering output).
In conclusion, there has not been provided a magnetic recording medium having excellent running property without increasing head clogging.